Have you ever wondered what animals dream about? When mice slumber, their rapid eye movements reflect the imagined movements of their heads in their dreams.
If the same is true for humans, researchers may be able to observe people walking around in their dreams by tracking their eye movements.
During a night鈥檚 sleep, people progress through different stages, from light dozing to heavy slumber. This includes several periods known as rapid eye movement (REM) sleep, when their eyes move jerkily from side to side.
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REM sleep is also when we have our most vivid dreams, something discovered in the 1950s. But it has long been unclear whether the accompanying eye movements have any significance or if they are entirely random.
and at the University of California, San Francisco, wondered if they could shed some light on this by putting electrodes into the brains of mice to record the firing of neurons that keep track of the orientation of the head.
They first recorded the firing of these neurons while the animals were awake and moving around. Using a camera fixed to the top of the head, they found that the mice鈥檚 head movements to the left or right were accompanied by fast, jerky movements of their eyes in the same direction.
The amount that their eyes moved to the left or right also tallied with the degree to which their heads turned.
The researchers continued recording when the mice fell asleep 鈥� luckily, mice sometimes sleep with their eyes open.
Sure enough, when the animals entered REM sleep, their jerky eye movements also correlated with the firing of the head-direction brain cells. In effect, the team could decode the mice鈥檚 dreams, at least to the extent of knowing which direction they were looking in.
鈥淲e were happy to see you can predict the change of head direction and its amplitude. It was pretty surprising,鈥� says Senzai.
This suggests that, in future, researchers could decode this aspect of rodents鈥� dreams without having to put electrodes into their head, just by tracking their eye movements, says Senzai.
at Erasmus University Medical Center in Rotterdam, the Netherlands, says the finding answers a long-standing question about whether eye movements in REM sleep are random 鈥� and could allow better understanding of human dreams.
Previous work in which electrodes were put into the brains of rodents has shown that during sleep, they 鈥�replay鈥� their movements around a laboratory maze, and this appears to help them to memorise its layout.
Something similar seems to go on in humans, and eye movements of people can be tracked while they sleep by placing electrical pads next to their eyes, avoiding the need to do brain surgery. 鈥淚t opens up new fields of research,鈥� says Canto.
Other researchers have tried to decode people鈥檚 dreams by attempting to have conversations with lucid dreamers, people who can control their dreams.
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